Plus do any of them even know how to 'tame' a dragon? Harry fought one back in GOF so at least he sort of knows how they behave but both Ron & Hermione are inexperienced. At least we can rely on Hermione's wits to help them escape but Ron mostly had to rely on both of his friends but he's brave enough to even try to handle a dragon so that's the Gryffindor in him.
